When full, containers of the specified type present significant rigidity that then prevents them from withstanding even relatively limited external or internal forces without damage.
Thus, an external force applied axially on the neck of a container of that type (e.g. when too many containers are stacked one on top of the other—typically packs of bottles stacked on pallets—) can cause the wall made of plastics material to kink at the shoulder of the container, below the neck; as a result the neck enters, in part, into the shoulder, generally on one side of the container, such that the neck thus slopes significantly relative to the axis of the container. Often, the wall does not rupture and liquid therefore does not leak out, and the content of the container can be used. However, customers always reject containers damaged in this way, which thus become unsellable.
In addition and above all, when a container of the type under consideration is filled with a hot liquid and is then closed, air that remains trapped in the container decreases slightly in volume on cooling down. This typically occurs with containers that are filled in high-speed filling installations, in which the containers are closed well before the liquid that was poured in hot has cooled down to ambient temperature. The shrinkage in the volume of the air during cooling thus places the inside volume of the container in a state of reduced pressure.
For the container to be able to withstand this reduced pressure without deforming, it needs to present sufficient mechanical rigidity, which means that it has thick walls for example; in other words, such a container requires more raw material and is therefore more costly, which is not acceptable to producers of packaged liquids. It is indeed known to manufacture containers having a body that is specially configured (a paneled body) so as to be able to support such reduced pressure without visibly deforming. However, such specially-shaped containers are also significantly more costly than conventional containers.
However, if the container is not strong enough, it deforms in uncontrolled manner, and, once again, its unattractive appearance makes it difficult to sell.
There thus exists an urgent need for containers of conventional shape, typically for bottles having a substantially cylindrical general shape, but that are suitable for withstanding forces, at least to some extent, without substantially deforming in uncontrolled manner, in particular when being filled with a hot liquid, and without notably adding to the cost of the container.